Light emitting diode illumination system

ABSTRACT

In various embodiments of the invention, a unique construction for Light Emitting Diodes (LEDs) with at least one luminescent rod and extracting optical elements is used to generate a variety of high brightness light sources with different emission spectra. In an embodiment of the invention, forced air cooling is used to cool the luminescent rod. In an embodiment of the invention, totally internal reflected light can be redirected outward and refocused. In another embodiment of the invention, light emitted by the luminescent rod is out-coupled for use in a variety of applications. In various embodiments of the invention, a plurality of independent narrow band colors can be coaxially combined.

PRIORITY CLAIM

This application claims priority to: (1) U.S. Provisional PatentApplication Ser. No. 60/954,140, entitled: “LIGHT EMITTING DIODEILLUMINATION SYSTEM”, inventor: Thomas J. Brukilacchio, filed Aug. 6,2007, which application is incorporated herein by reference in itsentirety.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to the following application, which wasfiled on Aug. 5, 2008 herewith:

“LIGHT EMITTING DIODE ILLUMINATION SYSTEM” by Thomas J. Brukilacchio,application Ser. No. 12/186,475, which application is incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

This invention, in general, relates to high brightness illuminationsources and more particularly to the use of Light Emitting Diodes (LEDs)as a source of illumination.

BACKGROUND OF THE INVENTION

There is a significant need for high brightness broad band illuminationsources to provide optical fiber coupled illumination for surgicalendoscopy and other applications where extremely high brightness sourcesare needed such as in projection systems and high speed industrialinspection. Prior art typically utilize short arc lamps such as highpressure mercury, metal halide, and xenon. These lamps are capable ofvery high luminous emittance and are therefore suitable sources for theetendue limited fiber optic coupled illumination systems. Approximately85% of the high brightness illumination sources in use in the operatingroom today are based on compact short arc xenon lamps. The problemsassociated with these lamp technologies, however, include poor luminousefficacy thereby requiring high power and associated means of cooling,short lifetime, high voltage operation (typically kilovolts required toturn them on), high cost, and use of mercury which is becoming anenvironmental hazard and is in the process of undergoing regulations innumerous countries throughout the world.

Only recently has there been recognition that Light Emitting Diodes(LEDs) may provide sufficient illumination to be used to replace moretraditional light sources in endoscopic illumination systems. Inparticular, LEDs provide much improved lifetime, lower cost ofownership, lower power consumption (enabling some battery operatedportable devices), decreased cooling requirements, and freedom formmercury relative to conventional arc lamps. Additionally they can bereadily modulated which can be a significant advantage in manyapplications. To date no LED based endoscopic illumination systemcommercially exists that equals or exceeds the luminous intensity of thecompact xenon arc lamp systems. The invention described herein has thepotential of meeting and exceeding the output of the best arc lampssystems available today

BRIEF DESCRIPTION OF THE DRAWINGS

This invention is described with respect to specific embodimentsthereof. Additional features can be appreciated from the Figures inwhich:

FIG. 1 shows an embodiment of the light emitting diode illuminationsystem, where three spectral coupled sources are combined to provide ahigh brightness light source;

FIG. 2 is a detail of the solid rod luminescense material optical systemcomprised of the luminescent rod, LED excitation sources, heat sinks,and index matched output optic. The top view represents a crosssectional view;

FIG. 3 shows an embodiment of the invention with the combined mirror andcooling system;

FIG. 4 shows an alternative embodiment of the invention containing twoluminescent rod sources in series;

FIG. 5 shows various alternative cross sectional shapes according todifferent embodiments of the invention;

FIG. 6 shows three different output coupling optics attached to theluminescent material rod and integrated as part of the rod according tovarious embodiments of the invention;

FIG. 7 shows a plot of efficiency of coupling light out of the end ofthe rod assuming different cross sectional shapes (_circular vs - - -square) as a function of the index of refraction of the attached optic;

FIG. 8 shows the transmission spectrum of a white light source as afunction of wavelength for two thicknesses (1 mm and 50 mm) for a 0.15%doped Ce:YAG rod;

FIG. 9 shows a spectral plot of the relative intensity versus wavelengthfor three sources (blue, green and red) in the system of FIG. 1;

FIG. 10 shows a means of combining (A) a laser beam, specifically adirect laser diode, with the other colors in order to increase the colorpalette of a light engine, and (B) two laser beams, according to anembodiment of the invention to create a 6 color light engine (see FIG.13);

FIG. 11 shows a truncated ball lens for coupling to a luminescent rodaccording to an embodiment of the invention;

FIG. 12 an end view of a luminescent rod excited by two arrays of LEDsin which there is a column of forced air that forced between the rod andthe LED surface through a controlled airspace according to an embodimentof the invention;

FIG. 13 shows a six color light engine layout, including a luminescentrod, two laser diodes and three other solid state light sources, withdichroic mirrors to create a single coaxial 6-color beam according to anembodiment of the invention;

FIG. 14 shows a four color light engine layout, including a luminescentrod and three other solid state light sources, with dichroic mirrors tocreate a single coaxial 4-color beam. Each individual light source iscollimated so as to be efficiently combined and after color combinationthe beam is refocused into a light guide for transport to the device orsystem to be illuminated according to an embodiment of the invention;

FIG. 15 a resulting spectrum with four color bands combined alongside astandard fluorescence microscopy emission filter, according to anembodiment of the invention which provides narrow band illuminationregions that do not overlap with the spectral regions of interest tobio-analysis; and

FIG. 16 shows a six color result, according to an embodiment of theinvention to realize a versatile light engine for life science analysiswith narrow bands spread across the visible spectrum with nearly thesame optical energy available in each band.

DETAILED DESCRIPTION OF THE INVENTION

Prior to LED based systems conventional arc lamp based projectionsystems were used comprised of a short arc lamp typically of the highpressure mercury, metal halide, or xenon lamp variety. The primarydisadvantage of the short arc technology is lamp life, which istypically in the 500 to 1000 hour range. The cost of the arc lamp itselfand the service cost to replace the lamps over the life of the productcan be many multiples of the original cost of the complete illuminationsystem. The arc lamp needs time to stabilize, so tends to be left on forhours, even when the actual usage time is minutes, so that 500 hours canbe accrued in a few months of usage. Additional benefits of the LEDtechnology include reduced power consumption, low voltage operation,light intensity stability, no warm-up period is required, ability tocontrol correlated color temperature (CCT) and color rendering index(CRI), and the ability to modulate the source. The ability to modulatethe source can be a significant benefit. For example, most of theendoscopic systems in use today are coupled to a video camera. Typicallyvideo cameras incorporate an electronic shutter and typically the videosignal is not integrated continuously. Thus, there is an opportunity tomodulate the LED source in synchronization with the shutter. During thetime when the shutter is closed, the LED light source does not need tobe on. Thus, for example, if the shutter was open 50% of the time, thelight source can be modulated in synchronization producing 50% lessheat. Thus, for the same average input power to the LED light source thelight output can be increased by an amount dependant on the operatingpoint of the LED source with respect to efficiency.

A more conventional approach to producing white light by LEDs is todeposit a phosphor powder, typically of Ce:YAG (cerium doped yttriumaluminum garnet, Y₃Al₅O₁₂:Ce³⁺) suspended in an encapsulant materialsuch as silicone, onto a blue LED die or die array with a peakwavelength between about 445 nm and 475 nm. The light absorbed by thephosphor is converted to yellow light, which combines with the scatteredblue light to produce a spectrum that appears white. The apparent colortemperature is a function of the density and thickness of the phosphorsuspended in the encapsulant. While this approach is efficient, theamount of white light produced per unit area per unit solid angle isfundamentally limited by the amount of blue light extracted from theblue LED die or die array, the quantum efficiency of the phosphor, thephosphors thermal quenching, and the back scattering, which is afunction of the particle size of the phosphor or other luminescentmaterial. While it is feasible to place a solid phosphor such as singlecrystal Ce:YAG over the top of the blue LED die or die array, theefficiency of such a device would be limited by the total internalreflection of such a luminescent material due to its high index ofrefraction and more importantly, the reduction due to Stokes and quantumefficiencies, scattering and back-emission reduce the quantity of lightand this is contradictory to the goal of producing high brightness.

In various embodiments of the invention, a white light or multi-colorillumination system incorporates a luminescent rod material which isexcited along its length by a linear array of LEDs. In an embodiment ofthe present invention, the luminescent material is a single crystal. Inan alternative embodiment of the invention, the luminescent material isa sintered ceramic Ce:YAG (cerium doped yttrium aluminum gamete,Y₃Al₅O₁₂:Ce³⁺) and the LEDs are blue GaN based surface emitting devices.In an embodiment of the invention, the green and/or yellow outputspectrum from the rod can be coupled to a collection optic whichconverts the light emitted from the aperture of the rod to a largerdimension with a smaller solid angle. In an embodiment of the invention,the light emitted can be imaged to a fiber bundle or other lighttransporting medium such as a liquid light guide (LLG). In an embodimentof the invention, the output of the luminescent rod and collection opticcan be combined with the output of other directly coupled LED arrays inthe blue and red spectral regions to produce white light. In anembodiment of the invention, the outputs of two or more luminescent rodsubsystems may be combined to produce desired spectra of nearlyunlimited shape. In an embodiment of the invention at least fournon-overlapping narrow color bands can be combined into a single coaxiallight bundle. In an embodiment of the invention a six color illuminationsystem can be obtained, by adding at least one laser diode to at leastone luminescent rod subsystem and combining with other solid state lightsources. In an embodiment of the invention all of the independent andnon-overlapping spectral bands are produced by using LEDs and laserdiodes, in concert with at least one luminescent rod to enhance thebrightness of the delivered light and all such channels are capable ofelectronic intensity control, electronic shuttering and can be modulatedat rates exceeding 10 KHz (we need to add details for all theseembodiments if we wish to claim them!!)

Blue and red LED modules can be produced to equal or exceed thebrightness of conventional high brightness light sources such as compactxenon arc lamps. However, the efficiency of LEDs in the true greenspectrum, especially in the spectral region of 555 nm are ofcomparatively low efficiency and are not sufficiently bright compared toarc lamps. Typically light generated from LEDs in the spectral region of555 nm is achieved by applying a thin layer of directly over LED dieemitting blue light. The light from the phosphor particles is partiallyabsorbed and partially scattered. A combination of the scattered bluelight and the absorbed light re-emitted as luminescent light at longerwavelengths typically in the green and red spectral regions, produceswhite light. It is possible to increase the thickness of the phosphorlayer to fully extinguish the blue LED excitation energy but the totalamount of green and/or red light produced by the phosphor, is reduceddue to the increased back-scattering of the thicker phosphor layer andthus a green LED made of a blue LED with a green phosphor is far lessefficient than a direct bandgap green (e.g. InGaN) LED. In particularthere are high efficiency laser diodes at wavelengths aboveapproximately 620 nm and below approximately 410 nm. For the green andyellow regions, there are a wide variety of diode-pumped solid state(DPSS), frequency doubled YAG lasers but these light sources havenumerous problems of manufacture, temperature-control requirements andare expensive. Furthermore, it is not always desirable to havesingle-wavelength coherent light for bio-analytical work. Thus, aluminescent rod with a broad emission band output spectral shape (20 to150 nm) can be extremely useful for exciting a range of fluorophorescovalently attached to analyte molecules.

The amount of white light produced can be increased by increasing thecurrent density to the LED up to the point where the output of the LEDrolls over and no longer increases with increasing current. Thebrightness of any LED made by in this general configuration isfundamentally limited by the internal and external quantum efficiency ofthe LED die, the quantum efficiency of the luminescent material, theamount of scattering by the particles, the thermal quenching propertiesof the die, and the die junction temperature.

In contrast, the present invention is not limited by the current densityof the LED as the length of the rod material can be increased toincrease the number of excitation LED die and thereby increasing theluminescence output. For example, a high performance LED die with a 1 mmsquare area coated with a high performance phosphor can produceapproximately 200 Lumens with a heat sink temperature near roomtemperature at the maximum current density (i.e., before rolling overand no longer producing more light with further increases in currentdensity). Even with extraordinary cooling measures the phosphor-on-LEDapproach can yield at best green/yellow light densities of 500 mW persquare millimeter at best with the current state of the art blue InGaNLEDs. By contrast, with the present invention we have demonstratedgreater than 5 watts emitted from the same size surface using aluminescent rod material.

In an embodiment of the invention, a luminescent rod with a 1 mm squarecross sectional area and a length of 50 mm can have approximately 100LEDs exciting the luminescent rod. In an embodiment of the invention, aconservative efficiency of 30% can result in an output of more than anorder of magnitude higher photometric power with each LED operating atcurrent densities significantly lower than the maximum current density.Furthermore, if higher output was required the length of the rod can beincreased along with an increase in the number of LEDs exciting theluminescent rod. Thus in various embodiments of the present invention, ameans of producing output in the green portion of the spectrum resultsin higher brightness than can be achieved by even the best xenon shortarc lamps.

The present invention relates to high brightness illumination systems.In particular, the present invention represents an LED based lightsource for improved illumination systems relative to arc lamp and otherLED based light source systems. In an embodiment of the invention, theillumination system 10 of FIG. 1 is comprised of one or more LED die ordie array modules 12, 24 and 26 spectrally and spatially combined bymeans such as dichroic beam splitters 42 and 44 coupled to a commonsource aperture 52 which substantially conserves the etendue or area,solid angle, index squared product. In an embodiment of the invention, aluminescence rod system couples into an optical fiber bundle to providethe high luminous power and high brightness required for bioanalyticaland medical endoscopic applications. Other high brightness applicationsinclude, but are not limited to, projection systems, industrialillumination, photo curing, spot lights, and medical photodynamictherapy.

In FIG. 1 the LED source module 12 is comprised of a central rod 14 ofluminescent material such as single crystal or sintered ceramic Ce:YAG,and other luminescent materials including(Lu_(1-x-y-a-b)Y_(x)Gd_(y))₃(Al_(1-z-c)Ga_(z)Si_(c))₅O_(12-c)N:Cea_(a)Pr_(b)with 0<x<1, 0<y<1, 0<z</=0.1, 0<a<=0.2, 0<b<=0.1, and 0<c<1 for exampleLu₃Al₅O₁₂:Ce³⁺, Y₃Al₅O₁₂:Ce³⁺ and Y₃Al_(4.8)Si_(0.2)O_(11.8)N_(0.2):Ce³⁺emitting yellow-green light; and(Sr_(1-x-y)Ba_(x)Ca_(y))_(2-z)Si_(5-a)Al_(a)N_(8-a)O_(a):Eu_(z) ²⁺ where0<=a<5, 0≦x<=1, 0<=y<=1, and 0<z<=1 for example Sr₂Si₅N₈:Eu³⁺, emittingred light. Other candidates include(Sr_(1-a-b)Ca_(b)Ba_(c))Si_(x)N_(y)O_(z):Eu_(a) ²⁺ where a=0.002 to0.20, b=0.0 to 0.25, c=00 to 0.25, x=1.5 to 2.5, y=1.5 to 2.5, and z=1.5to 2.5 for example SrSi₂N₂O₂:Eu²⁺;(Sr_(1-u-v-x)Mg_(u)Ca_(v)Ba_(x))(Ga_(2-y-z)Al_(z)In_(z)S₄):Eu²⁺ forexample SrGa₂S₄:Eu²⁺; (Sr_(1-x-y)Ba_(x)Ca_(y))₂SiO₄:Eu²⁺ for exampleSrBaSiO₄:Eu²⁺; (Ca_(1-x)Sr_(x))S:Eu²⁺ where 0<x<=1 for example CaS:Eu²⁺and SrS:Eu²⁺;(Ca_(1-x-y-z)Sr_(x)Ba_(y)Mg_(z))_(1-x)(Al_(1a+b)B)Si_(1-b)N_(3-b)O_(b):RE_(n)where 0<=x<=1, 0<=y<=1, 0<=z<=1, 0<=a<=1, 0<=b<=1 and 0.002<=n<=0.2 andRe is either europium(II) or cerium(III) for example CaAlSiN₃:Eu²⁺ orCaAl_(1.04)Si_(0.96)N₃:Ce³⁺; andM_(x)V+Si_(12-(m+n))Al_(m+n)O_(n)N_(16-n), with x=m/v and M comprised ofa metal preferably selected from the group comprising Li, M, Ca, Y, Sc,Ce, Pr, Nf, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or mixtures includingfor example Ca_(0.75)Si_(8.625)Al_(3.375)N_(0.625):Eu_(0.25) asdisclosed in U.S. patent application Ser. No. 11/290,299 to Michael R.Krames and Peter J. Schmidt (publication #2007/0126017) which is hereinexplicitly incorporated by reference in its entirety; and nano-phosphorsembedded in a suitable matrix such as high index plastic or glass, withLED die positioned along its length in a linear array of die or a singlelong LED die attached to a high thermal conductivity board 18, such ascopper or aluminum core printed circuit board, which in turn is attachedto heat sink 20. In an embodiment of the invention, the luminescent rod14 can have the properties of high absorption of light in one part ofthe spectrum, blue in the case of Ce:YAG, emission with high quantumyield in a wavelength region generally longer than the excitationwavelength band, high index of refraction to trap a significant portionof the luminescent light produced such that it is guided or transmitteddown the length of the rod toward an emitting aperture 52. In anembodiment of the invention, the emitting aperture can be index matchedto an optical concentrator 22 such as a compound parabolic concentrator(CPC), compound elliptical concentrator (CEC), compound hyperbolicconcentrator (CHC), taper, or faceted optic. The concentrators can beindex matched and made of solid dielectric. In an alternative embodimentof the invention, the concentrators can be index matched and made of aliquid dielectric. The purpose of the concentrator is two-fold. First,it would be made of a material with an index of refraction approachingthat of the rod (approximately 1.82 for Ce:YAG). Second, it would act toconvert the light emitted over a hemisphere (2π steradians) to an areaand solid angle that can be readily imaged through dichroic beamsplitters and re-imaging optics while substantially preserving theetendue (area, solid angle, index squared product) thereby maximizingthe brightness. In another alternative embodiment of the invention, alens can be used rather than an optical concentrator. A ball lens isespecially useful as it can reduce the angular extent of the lightsource, allowing for simpler optical collection into or onto the desiredtarget area. In many cases the optical index matching need not beperfect. In an embodiment of the invention, a suitable commerciallyavailable low index material (n˜1.46) coupling gel can be appliedbetween the luminescent rod and the half ball lens with resulting 80 to90% extraction efficiency. With YAG:Ce as the luminescent material and ahalf ball lens of somewhat higher index, e.g. Schott type SF6 glass orS-LAH79 from Ohara, as much light as is trapped by the TIR light-guidingmechanism can be extracted, i.e. all the light that is guided withinabout a 57 degree half angle within the YAG medium.

In an embodiment of the invention, the output spectrum of the Ce:YAG rodsource can cover the range between about 500 nm and 700 nm, with thepredominant contribution in the green spectrum centered around 555 nm.In an embodiment of the invention, the combination of the light from aluminescent rod with that from a blue LED module 24 can produce whitelight suitable for many applications. For bioanalytical and medicalillumination applications, however, the relative spectral content istypically required to result in a high color rendering index (CRI) onthe order of 85 or greater. To accomplish this it is necessary to addadditional light in the red spectral region from a third LED sourcemodule 26. In FIG. 1 dichroic beam splitter 42 can transmit the redlight of LED module 26 and reflect the blue light of LED module 24.Dichroic beam splitter 44 can transmit the combined blue and redspectrum of combined LED modules 26 and 24 and reflect the green oryellow light of LED module 12. The combined white light spectrum fromLED modules 12, 24, and 26 can then be imaged by lens elements 46 and 50to fill the input aperture 52 of fiber optic light bundle 54. The lenselements 46 and 50 can be comprised of multiple lens elements which caninclude glasses or plastics of different dispersions to help optimizeimage quality. The lens systems aperture stops 48 can assure that theextent of the far field of the light from each LED module was similar soas not to result in color fringe effects at the edge of the illuminationfield. In particular in a microscope illuminator, when the Kohler methodis utilized, each colored component should have the same far fielddistribution as the pupil of the illuminator is being imaged onto thebiological specimen. The size of each LED source and its collectionoptics can be sized such as to produce substantially similar near andfar field distributions for each LED module. The lens system can alsoinclude diffractive or reflective components to help reduce the numberof or optical elements and to reduce overall package size. The relativeposition of the LED modules 12, 24, and 26 can be interchanged assumingthat the dichroic beam splitters were changed in spectralcharacteristics to accommodate different arrangements. For example, LEDmodules 12 and 24 can be switched in position such that beam splitter 42can transmit red light, reflect blue and green light and beam splitter44 can transmit red and green and reflect blue light. The spectrum ofthe LED modules in a different system can include ultraviolet throughmid infrared light assuming the optical elements were made of the propertransmitting materials and anti-reflection or reflection coatings. In anembodiment of the invention, the LED modules 24 and 26 can be comprisedof a LED array index matched to the collection optic depending on theextraction efficiency and brightness of the LED die. The collectionoptics can be comprised of similar optics as detailed for the LED module12, the optical concentrator, or alternative optics can be designed forindex matching. In an alternative embodiment of the invention, the LEDmodules 24 and 26 can be comprised of a LED array not index matched tothe collection optic again depending on the extraction efficiency andbrightness of the LED die. The collection optics can be comprised ofsimilar optics as detailed for the LED module 12, the opticalconcentrator, or alternative optics can be designed for no indexmatching. For example blue die from CREE (EZ1100) includes a micro lensarray such that the benefit from index matching does not compensate forthe increase in the etendue due to the index squared effect. Thus forthe case of these high performance blue color dies, higher brightness isachieved by not index matching. In contrast, the red dies that arecurrently commercially available do not typically includemicrostructures on their surface to significantly enhance extractionefficiency and thus do benefit from encapsulation, not from a brightnessstandpoint, but from an efficiency standpoint which due to decreasedthermal load translates into improved performance. For the abovediscussion, white light can consist of a combination of discretewavelengths and/or discrete color bands and/or a continuous mix of suchwavelengths spanning the ultra-violet visible infrared spectrum.

In various embodiments of the invention, heat sinks 12, 25, and 34 ofFIG. 1 can be made out of any high thermal conductivity materialincluding but not limited to copper and aluminum. The LED or LED arrays16, 30, and 38 can be attached to LED printed circuit boards (PCBs) 18,28, and 36 which can in turn be thermally and mechanically attached toheat sinks 12, 25, and 34 respectively. In various embodiments of theinvention, the PCBs can be made out of a high thermal conductivitymaterial including but not limited to copper, diamond, aluminum, orcomposite materials. In various embodiments of the invention, thethermal resistance between the back side of the LED die or die arrayscan be minimized by direct eutectic attachment, soldering, or a thinlayer of thermally conductive epoxy such as Diemat 6050. The highthermal conductivity PCBs can act as heat spreaders thereby reducing theheat flux density into the heat sinks 12, 25, and 34. The heat sinks canbe cooled by direct convection with air, conduction with various coolantfluids such as water, or radiation into the surrounding environment.Heat pipes of various constructions have also been found to work veryeffectively as heat spreaders. Heat pipes and diamond can also be usedas the PCB material as they both are very effective heat spreaders withperformance well above that of pure copper.

FIG. 2 shows a detailed view 60 of the LED module 12 of FIG. 1 from theside and in cross section as indicated in 70. In an embodiment of theinvention, the luminescent rod 14, can be a single crystal. In analternative embodiment of the invention, the luminescent rod 14, can bea transparent sintered polycrystalline Ce:YAG. In various embodiments ofthe invention, the luminescent rod 14 can be characterized by highabsorption in a spectral region such as blue in the region of 460 nm andvery low extinction for wavelengths greater than the excitationwavelength band above 500 nm to 510 nm. The rod material 14 can also becharacterized by exhibiting luminescence of the absorbed excitationlight with high quantum yield. In an embodiment of the invention, theLED array 16 can be comprised of a blue LED die such as thosemanufactured by CREE Inc. called EZ1000, which are dimensionally on theorder of 1 mm square by 0.120 mm thick. The light from the LED array canbe transmitted through the outer wall of luminescent rod 14. Theabsorption coefficient of the luminescent rod 14 can be chosen to befairly high, i.e. it can be doped to a level resulting in substantiallyall of the blue light being absorbed within the dimension of the rodprior to exiting the rod through its other side. To the extent that theexcitation light was not absorbed with the first pass through the rod14, mirrors 72 can be positioned with a reflective surface close to therod so as to cause the excitation light to pass back into the rod one ormore times to maximize absorption by the rod. The reflectivity of theLED die is on the order of 80%, which can also act to couple light thatwas not absorbed on the first pass through the rod back into it foranother opportunity to be absorbed. The light can take multiple passesto be substantially absorbed. Given the finite reflectivity of themirrors 72 and diffuse reflectivity of the LED die 16 it can be best tochose an extinction that can result in the order of 80% or more of theexcitation light being absorbed on the first pass through the rod 14. Itis also useful to place the LED surfaces as close to the rod as may bepractical, while still allowing some air flow between these elements. Inan embodiment of the invention, the LED surface is approximately 200microns from the rod to ensure high excitation efficiency. In analternative embodiment of the invention, the LED surface isapproximately 120 to 320 microns from the rod. In this situation, areasonable mechanical alignment tolerance corresponds to ±20 microns. Inan alternative embodiment of the invention, the sides of the rod throughwhich the excitation light is not passing initially can be coated with ahigh reflectivity coating. In this embodiment, the reflectivity can bevery close to 100% so as not to lose substantial luminous power uponmultiple reflections as the luminescent light is transmitted toward theoutput aperture 62. In another alternative embodiment of the invention,the outside surface of the rod can be not coated at all so as to allow asubstantial portion of the light generated within the rod to be guidedby total internal reflection (TIR) up the rod toward output aperture 62.In this embodiment, the fact that the luminescent material 14 has arelatively high index of refraction is fortunate as the higher the indexof refraction the greater percentage of the light that is generatedwithin the rod will be guided by TIR toward the output aperture 62.

The luminescent light generated within the rod 14 would be substantiallyisotropic and thus would travel equally in all directions. Thus half ofthe light that is bound to the rod by TIR would travel in a directionopposite to the output aperture 62 toward mirror 66 which can act tosend the light emitted in that direction back toward output aperture 62,thereby substantially doubling the light reaching output aperture 62.The mirror can also be effectively coated directly onto the end face ofrod 14 in the vicinity of mirror 66.

FIG. 3 shows an alternative embodiment 80 of the mirror elements 66 ofFIG. 2 comprised of modified mirror elements 82 containing the additionof small holes 84 through which high pressure air can cool rod 14 byhigh pressure air impingement. The holes can be sufficiently small as tominimally affect the mirrored surface area of mirrors 82. High pressureair impingement has several times the film coefficient and thus heattransfer as compared to standard convected low pressure air. The effectof the slight increase in the index of refraction of the mediumsurrounding rod 14 on TIR can be minimal. If a direct contact coolingfluid was used without the sides of the rod being reflective, the higherthan air index of refraction of the fluid can result in more loss outthrough the sides due to the decreased TIR internal angle, therebyreducing overall LED module efficiency. The reason it can be importantto provide a means of removing heat build up from the rod is that therecan be a small but finite heat absorption, convection and conduction tothe rod from the LED array 16 that can cause an increase in temperatureof the rod if there were no means of removing this heat. This heat risecan result in reduced overall performance due to thermal quenching ofthe luminescent rod material. Increasing the temperature of the rodmaterial can decrease the quantum efficiency.

FIG. 4 shows an alternative embodiment 120 of LED module 12 of FIG. 1where two modules 12 have been positioned in sequence to form a singlemulti-spectrum source. For example rod 122 of 120 can be made of aluminescent material with properties similar to those described for rod14 for which the excitation band is within the long wavelengthultraviolet spectrum in the region of 240 nm to 420 nm. The hightransmission region of the material can be in wavelengths longer than420 nm and its luminescence can be in the blue to blue-green spectralregion. Likewise rod 124 can have similar absorption properties butcomprise luminescence in the green to red region of the spectrum. Bothrods 122 and 124 can be characterized by high transmission in thespectral region containing wavelengths longer that 420 nm.

In an embodiment of the invention, the mirror 66 can act to reflect anylight transmitted in the direction opposite output coupler 22 backtoward 22. In this way, LED light module 120 can contain the full anddesired spectrum of the white light source and can require neithersupplemental LED modules 24 and 26 of FIG. 1 nor dichroic beam splitters42 and 44. In an embodiment of the invention, an index matching materialbetween the two rods 122 and 124 such as melted Schott SF6 glass orother suitable index matching material can be used. In an alternativeembodiment of the invention, a single material or ceramic such as YAG(yttrium aluminum garnet) can use different dopants in the regionscorresponding to rods 122 and 124 such that the rod is continuous andthere is no need for an index matching medium. In another alternativeembodiment of the invention, more than one dopant can be used evenlyover the entire length of a single rod assuming the dopants did notinterfere and reduce quantum efficiency. The length of the rods andexcitation LED arrays can be increased to achieve higher flux out ofcollection optic 22. In various embodiments of the invention, anadvantage of this technology over thin planar luminescent materialcoated on a LED, is that the output can be increased by increasing thelength of the rod rather than increasing the power density of theexcitation source thereby resulting in output flux many multiples ofthat which can be achieved by prior art. In an alternative embodiment ofthe invention, the output of the system of FIG. 4 can be directlycoupled to an optical fiber bundle without the need for re-imagingoptics.

In various embodiments of the invention, alternative cross sectionalareas for rods including but not limited to circular, square,rectangular, and multiple sided polygons such as a hexagon and octagonare shown in FIG. 5. Generally, even number of sides polygons havebetter spatial mixing than those with an odd number of sides althougheither can be used. Likewise, the optical concentrator that can be indexmatched to one of the rod configurations can have a similar crosssectional shape. For example a rectangular or square CPC or taper can beused. A theta by theta CPC comprised of a taper coupled to a CPC such asdescribed by Welford and Winston (“High Collection Nonimaging Optics”,W. T. Welford and R. Winston, Academic Press, 1989) can be used.

FIG. 6 shows various configurations 100 of a combination of luminescentrod and output concentrators. For example the rods 102, 108, and 114,can be index matched to output couplers in the form of a taper 104, CPC110, or combined theta by theta taper and CPC 116. In general theconcentrators can be made out of a material that is transparent and ofsimilar index of refraction and can be coupled by means of an indexmatching medium. Alternatively, the two components comprising a rod andconcentrator can be mated by heating the components under pressure,causing them to melt together. Alternatively, the rod and concentratorcan be made out of the same material such as ceramic (phosphor particlessintered at temperatures on the order of 1800° Celsius and underpressure causing the material to become transparent and substantiallyhomogeneous) such as Ce:YAG which can be doped in the region of the rodand not doped in the region of the concentrator thereby eliminating theneed for index matching.

FIG. 7 shows a plot of index of refraction of the concentrator versuscoupling efficiency for the case of a Ce:YAG rod which has an index ofrefraction on the order of 1.82 for two rod geometries circular andsquare in cross section. The out-coupling efficiency into air (index ofrefraction 1) of 30% assumes that all the light emitted by the LED dieis absorbed within the rod and that one end of the rod is coated with amirror with reflectivity of 100%. Thus, the efficiency can be at leastdoubled, up to the limit of the light-guided available efficiency ofabout 70% for a luminescent rod having this index, by index matching toa concentrator with an index of refraction approaching that of the rod.The data assumes that the output face of the concentrator is coated tominimize losses due to Fresnel reflections at the air/glass interface.

FIG. 8 shows empirical data for a white light source transmitted throughthe side of a Ce:YAG rod of 1 mm thickness and guided down a length of50 mm. The Cerium doping was 0.15%. The data shows that for the 1 mmpath length more than 90% of the blue light was absorbed. The 50 mm rodwas not coated, so the maximum expected transmission of blue light goinginto the rod would be on the order of 84% due to Fresnel reflectionwhich is observed at a wavelength of about 400 nm where the Ce:YAG rodis substantially transparent. The fact that the output is above theexpected maximum transmission for wavelengths greater than 500 nm is dueto the contribution from the luminescent light emitted by the absorbedblue light in the incident white light. The broader absorption bandshown in the 50 mm length is due to the fact that Beer's Law is actingover 50 times the length exponentially. It is also apparent that thematerial does exhibit some degree of self absorption for which some ofthe absorbed light emitted as phosphorescence is absorbed through thelength. Thus for some applications it can be important to limit thelength of the rod to minimize absorption at the short end of the emittedspectrum and to minimize heating due to self absorption.

Thermal Considerations of Rod Handling

The rod might easily absorb 20 watts and only re-emit 15 W, due toStokes shift and material inefficiencies, leading to a fast heatingunless rather extreme cooling measures are undertaken. In an embodimentof the invention, a high pressure fan can be direct a thin column of airinto the gap between opposing surfaces (LED line arrays on opposingsides) as shown in FIG. 12. The air cooling is favored if the LEDs canbe spaced apart from the luminescent rod by about 200 microns (see FIG.12).

The rod may be any shape. In an embodiment of the invention the rod ispreferably square and polished highly with minimum chips so as to passthe maximum light, but without needing for example a ‘laser grade’finish. The cost of the rod is high but with reduced surface tolerancespecifications can be fabricated with relative ease and therefore such acomponent can be considered commercially viable. The density may beincreased and the length of the rod shortened and cost reduced (and thespectrum consequently widened due to reduced self absorption) if thethermal load can be managed. Other methods that can be used to managethe thermal load include contacting a suitable heat-spreading material,such as a large perforated metal fin or a ceramic material placed incontact with the rod. In an embodiment of the invention, thermalconsideration can be a primary concern in the overall design.

FIG. 9 shows the combined spectrum of the system of FIG. 1 with thethick black vertical lines representing the spectral region of thedichroic beam splitters. The driving current to the individual sourcescan be adjusted to result in a CRI greater than 90 at a CCT on the orderof 5700° Kelvin which is consistent with the values typical of short arcXenon lamps. The blue spectrum shown here is comprised of three blueLEDs with peak wavelengths centered around 445 nm, 457 nm and 470 nm.The red band is comprised of the combination of LED center wavelengthspeaked near 630 nm and 650 nm. The effect of increasing the spectralwidths in the blue and red spectral regions is primarily to increase theCRI.

The luminescence systems can be used for irradiating bioanalyticalinstrumentation including wells containing chemicals for inducingreactions or detecting reactants or products of chemical reactions. Thebioanalytical instrumentation can include a light source and fiber opticsystems for irradiating analytes within capillaries with selectedwavelengths of light and detecting luminescence produced by the analyteswithin the capillaries.

Separation by electrophoresis is based on differences in solute velocityin an electric field. The velocity of a charged analyte is a function ofits electrophoretic mobility and the applied voltage. The method ofelectrophoresis is used in a number of different techniques includingcapillary gel electrophoresis, capillary zone electrophoresis, micellarelectrokinetic chromatography, capillary electro chromatography,isotachophoresis and isoelectric focusing.

In general, the mobility of an analyte in a particular medium isconstant and characteristic of that analyte. The analytes mobility is aresult of two factors. The analyte is attracted to the electrode ofopposite charge, pulling it through the medium. At the same time,however, frictional forces try to prevent the analyte moving toward thecharge. The balance of these forces determines the actual overallmobility of the analyte. An analytes size, polarity and number ofelectric charge(s), relative hydrophobicity and ionic strength determinehow rapidly an electric field can move the analyte through a medium. Abuffer is used to assist the flow of the analyte relative to the field.The buffer's chemical composition, pH, temperature and concentrationalter the mobility of the analyte. Many important biological moleculessuch as amino acids, peptides, proteins, nucleotides, and nucleic acids,posses ionizable groups and, therefore, at any given pH, exist insolution as electrically charged species either as cations containing apositive (+) charge or as anions containing a negative (−) charge.Depending on the nature of the net charge, the charged particles willmigrate either to the cathode or to the anode. A small analyte will haveless frictional drag than a large analyte and hence move through themedium faster than a large analyte. Similarly, a multiply chargedanalyte will experience more attraction to the electrode and also movethrough the medium faster than a singly charged analyte. It is thisdifference in solute velocities that is responsible for the separatingeffect in electrophoresis that results in resolution of the speciesdetected.

Gel electrophoresis is a method that separates molecules such as DNA orproteins on the basis of their physical properties. A gel is a solidcolloid. Thus, gel electrophoresis refers to the technique in whichmolecules are forced to cross a span of gel, motivated by an electricalcurrent. Activated electrodes at either end of the gel provide theelectric field and thus the driving force for the migration of theanalyte. During electrophoresis, molecules are forced to move throughthe pores in the gel when the electrical current is applied. Their rateof migration, through the induced electric field, depends on thestrength of the field, their charge, their size and the shape of themolecules, the relative hydrophobicity of the molecules, and on theionic strength and temperature of the buffer in which the molecules aremoving.

One use of gel electrophoresis is the identification of particular DNAmolecules by the band patterns they yield in gel electrophoresis, afterbeing cut with various restriction enzymes. Viral DNA, plasmid DNA, andparticular segments of chromosomal DNA can all be identified in thisway. Another use is the isolation and purification of individual DNAfragments containing interesting genes, which can be recovered from thegel with full biological activity.

Capillary Zone Electrophoresis (CZE) replaces the gel in gelelectrophoresis with the combination of a buffer and a solid supportcontained within the capillary. In CZE, the analyte must move throughthe solid support contained within the capillary under the action of thebuffer, which is charged by the applied electric field. The buffer'schemical nature, pH, temperature, concentration and the presence ofsurfactant additives can be selected to assist in fully resolving (i.e.,spatially separating different analytes in the capillary with respect tothe time from introduction of the sample) different analytes in space(position in the capillary) with respect to time. Analytes separated byCZE can be detected based on absorption or fluorescence. Detection canbe carried out using on-column or fiber optic Z-cells.

In addition to electrophoretic techniques, separation of molecules canbe carried out in the absence of an applied field using chromatographictechniques. In liquid chromatography, the molecule dissolved in a buffercan still be charged, but rather than an electric field creating thedriving force, molecule migration is dependent on the flow of thebuffer. Frictional forces due to the interaction of the molecule with asolid support present in a column, act to prevent the molecule frommoving with the buffer. The molecule's size, hydrophobicity, and ionicstrength determine how rapidly the buffer can move the molecule througha medium. The buffer's chemical composition, pH, temperature andconcentration together with the nature of the solid support dispersed inthe column alter the mobility of the molecule. High performance liquidchromatography (HPLC) utilizes pumps to increase the flow of bufferthrough the columns resulting in high column backpressure, improvedresolution, increased flow rates and reduced analysis times. By reducingthe diameter of the column and/or increasing the length of the columnthe resolution can be improved. However, a problem with narrower columns(milli bore or micro bore) involves detection of the eluted species. Asthe diameter of the capillary in the narrow bore HPLC systems is furtherreduced, only a small number of molecules are available for detection ina small-defined area.

Microfluidic systems comprised of microfluidic chips, automated reagentdelivery apparatus and detection instrumentation are designed tominimize the users' effort in reagent delivery, reagent dilution and/ormixing, initiating chemical reactions and detecting those chemicalreactions in small volumes within highly automated environments. Amongthe numerous applications that exist, fluorescence is a commonly useddetection format. It is a sensitive and robust method for detectingenzyme assays, immunoassays, polymerase chain reaction (PCR),quantitative PCR, genomic sequencing among many other important chemicalreactions. Both homogeneous and heterogeneous reactions are suited tosuch devices and analysis is not limited by whether the reaction takesplace in free solution or on a solid support or within a narrow pore.Often microfluidic devices are produced by etching, molding or embossingchannels and wells into solid substrates (glass, silicon, plastic,etc.). Numerous layers of the device can be fabricated and then thelayers assembled to form the final analysis tool. Channels can be etchedin single or multiple dimensions enabling more complicated chemicalseparation and detection. Such devices can be used to introduce reagentsdirectly onto the chip or interfaced with automation equipment for suchpurposes. Like all fluorogenic detection, these systems require anexcitation source.

The present invention consists of one or more light sources in the formof a luminescent light pipe referred to herein as a lamp, in conjunctionwith relay optics for luminescence collection from an analyte forming aluminescence system for a volume interrogation apparatus wherein theinteraction of light with a chemical species located within or supportedon a solution volume can be the measure of the presence or quantitationof an analyte. Luminescence is defined as light not generated by hightemperature alone, typical of incandescence, including but not limitedto fluorescence and phosphorescence. Where high temperatures are definedas above approximately 2000° K. The analyte can be part of a reactioninvolving species including biopolymers such as, oligonucleotides (DNA,RNA iRNA, siRNA), proteins (including antibodies, enzymes, agonists,antigens, hormones, toxins), oligosaccharides and non polymeric speciessuch as steroids, lipids, phospholipids, small organic signalingmolecules (e.g., retinoic acid), pesticides and non peptidic toxins,hormones and antigens.

In alternative embodiments of the present invention, a luminescencesystem in conjunction with relay optics for luminescence collection,form a flexible and efficient system for a capillary/fluorescenceapparatus. In an embodiment of the invention, a plurality of lightsources and fiber optic systems separately and simultaneously irradiatea plurality of capillaries with selected wavelengths of light and thefluorescence produced by the molecules flowing within the capillariescan be separately and simultaneously detected. ‘Simultaneously’ isherein defined as occurring close in time. Two light pipes can irradiatetwo capillaries at the same time and the fluorescence from the moleculesin one of the capillaries can be delayed due to physical or chemicaleffects relating to absorption, phosphorescence and/or fluorescenceresulting in a delay in the fluorescence from the molecules in one ofthe capillaries.

In an embodiment of the present invention, a luminescence and collectionsystem can be adjusted for uniform luminescence of multiple capillariesor wells or a large area including numerous wells, spots or channels as‘detection volumes’. In an embodiment of the present invention,luminescence systems can irradiate an array of channels in an array ofcapillaries. In an embodiment of the present invention, an array ofchannels can be etched, molded, embossed into the capillaries. In anembodiment of the present invention, a set of wells intimately connectedto fluidic conduits can be stepped along the length of the fluidicconduit such that they can be interrogated at numerous sites for thepurposes of creating a map or image of the reacting species.

In an embodiment of the present invention, a luminescence and collectionsystem can irradiate an array of wells, spots and or an array ofchannels (be they etched, molded or embossed) or a set of wellsintimately connected to fluidic conduits such that they can beinterrogated at numerous sites for the purposes of creating a map orimage of the reacting species.

In an embodiment of the present invention, a luminescence and collectionsystem can irradiate homogeneous reactions within fluidic conduits orreservoirs; to irradiate heterogeneous reactions on the surface offluidic conduits or reservoirs; to irradiate homogeneous orheterogeneous reactions on the surface of or within the pores of aporous reaction support.

In an embodiment of the present invention, a luminescence and collectionsystem can emit multiple colors as desired. In an embodiment of thepresent invention, a luminescence and collection system can be pulsed onand off as desired to reduce heat generation. In an embodiment of thepresent invention, a luminescence and collection system can be pulsed onand off to allow time-based fluorescence detection.

In an embodiment of the present invention, a luminescence and collectionsystem can detect one or a number of reactions within the detectedvolume or volumes. The narrow band source of the light pipe drivenanalyzer provides better specificity, higher sensitivity, and lowerbackgrounds signals. The light pipe driven analyzer easily accommodatesmultiple wavelengths by additions of serially connected components.

In an embodiment of the present invention, a luminescence and collectionsystem can be pulsed on an off as desired to reduce or control heatgeneration and to allow time-based fluorescence detection.

In an embodiment of the present invention, luminescence systems canirradiate homogeneous reactions within fluidic conduits or reservoirs.In an embodiment of the present invention, luminescence systems canirradiate heterogeneous reactions on the surface of fluidic conduits orreservoirs. In an embodiment of the present invention, luminescencesystems can irradiate homogeneous or heterogeneous reactions on thesurface of or within the pores of a porous reaction support.

The light engine can be constructed to generate one or more colors. FIG.14 illustrates a four color light engine consisting of LEDs 1411 and aluminescent rod 1410. The output of each light source is filtered togenerated the specified spectral band using a band pass filter 1430,1440, 1450 and 1460 and then combined into one common optical path usingdichroic filters 1443, 1453, and 1463 positioned at 45 degrees. Theoutput from the rod is first out coupled using a truncated ball lens orother light extracting element 1420 and magnified by a plano convex lens1421. This light is then collimated by a asphere plano convex lens 1442.Similarly the output from the other light sources is collimated usingaspheres 1452, 1462, and 1472. The asphere lenses are designed so thatthe collimated light is generated and can pass through the bandpassfilters at nearly normal incidence, a requirement for optimum filterperformance. The light exits the light engine through a liquid lightguide 1490. Other embodiments include a optical adapters suitable forcritical illumination and Kohler illumination.

In FIG. 13 an embodiment is shown for a six color engine. A blue LED andcollimating optic 1330 is combined with a yellow LED and collimatingoptic 1360 and a cyan LED and collimating optic 1340 and these threewavebands combined with a luminescent rod and its associated collimatingoptic 1350, where only the light emitted by the luminescent rod 1350 isshown as beam 1390 (dotted line). Such four color combination is furthercombined with two laser diodes 1310 and all six color bands focused intoa light guide 1320 as described in FIG. 10.

Referring to FIG. 10(A), a laser diode 1010 which might be preferablyselected from a wavelength range of 630 to 650 nm, is pointed at a smallmirror 1040 to direct the light 1041 substantially in the oppositedirection from the main optical axis 1020 of the light engine. Said mainoptical axis 1020 already contains at least one color component such aswill be generated by using a luminescent rod excited by LED sources. Inone embodiment the red laser diode beam shape is sufficiently wide tocover a substantial portion of the collimator lens 1045 and the distanceof the divergent laser beam is substantially equal to the focal lengthof such collimating lens. The collimator may be a molded aspherical lensto reduce spherical aberrations. Directly thereafter the collimated redlaser beam strikes a dichroic mirror 1030 which is tilted slightly, inthe range of 2 to 8 degrees so as to redirect the laser beam back intothe collimating lens 1045, at near normal incidence, i.e. superimposed1043 and collinearly with the main optical axis 1020 of the lightengine. The red light is reflected at least 95% by said dichroic mirror,which passes substantially all of the main light engine beam, includingat least 90% of the filtered light that may result from utilizing aluminescent rod with a green or yellow narrow passband filter. The edgesteepness of the dichroic is particularly sharp because of the nearperpendicular usage of this edge filter. Such kinds of dichroic mirrorsare less ideal at, for instance 45 degrees where polarization effectsand angular walk-off cause poor edge steepness, so this construction hasparticular advantages for efficient color combination of multiple colorbands.

Referring to FIG. 10(B), two laser diodes 1060, 1061 can be combined asexplained in FIG. 10(A), and the small apparent source size allows thesebeams to be combined by a knife-edge (prism) 1042 such that both beams1046, 1047 can be refocused using dichroic mirrors 1031, 1032 into asuitably large light guide. For instance a 2 mm prism can be used withtwo red laser diodes 1060, to spatially combine the two sources (whichmay have different or identical wavelength output) into a 3 mm diameterentrance of a liquid light guide. An alternative embodiment can use alarger prism with apparent source positions coming from both sides ofthe optical centerline such that two different wavelength laser beamscan be directed toward the collimator lens, and after that, twodifferent dichroic mirrors utilized to reflect the two independentlasers back into the main optical axis, collinearly and overlappingly.For example a 405 nm laser diode can be directed as in FIG. 10(A), butfrom the opposing side and with a tilted dichroic, at an opposite tiltangle as shown in FIG. 10(B). In one embodiment a small prism is used tospatially combine two different wavelength laser diodes, such that theycan both be condensed, i.e. refocused, into the same light guide. In afurther refinement of the method, the prism combiner is mountedincluding some mechanical means 1080 onto a vibrating element 1090 suchas an audio transducer or piezo element or the like, which impartssufficient disturbance to both laser beams so as to cause a disruptionof the inherent speckle pattern to increase the uniformity andusefulness of the illumination for certain critical illuminationapplications.

In an embodiment of the invention, the two laser diodes combined can beof different colors. In an alternative embodiment of the invention, thecombining can be with a colored prism, holographic or other dichroic.

Notably each of the independent laser diodes can be directly modulated,turned on and off at high speed. It is also contemplated that a bandpassfilter or other optical element can be inserted between each laser andthe combining elements, for instance a heat rejection filter, to furtherimprove the light source for suitability for any intended application.

Optical Extraction Efficiency

In an embodiment of the invention, if the rod is coupled to the same orsimilar index material then it is logical to ‘out-couple’ through adome. FIG. 11 shows a side view of the luminescent rod 1130, where amirror 1110 is positioned at one end of the luminescent rod 1130, andbrackets 1120 constrain the rod 1130. Luminescence (dotted line) 1180from the rod 1130 exit the aperture and the coupling gel 1140 throughthe conical seat 1150 and the dome 1160 along the main axis compressiveforce 1170. In a frontal view, the dome is shown with the truncated balllens 1190. In such an embodiment, if the dome is sufficiently larger, onthe order of 3 to 20 times larger in diameter than the rodcross-section, the light will escape normal to the ray within thecrystal and emission of about 57 degree half angle can be expected forinstance for YAG:Ce. Out-coupling is defined as application of the sameor similar index material that is 3 to 20 times larger in diameter thanthe rod cross section, which can be shaped like a dome.

An unexpected result can be obtained with a modest index (napproximately 1.4 to 1.6) coupling gel or epoxy. In this contextapproximately corresponds to ±0.1. The thin layer is held in place bydirect compression via a back mirror (using the same or similar couplingmaterial if needed) and a spring. The mirror and ball lens are centeredon the crystal. The extraction is further enhanced if a truncated balllens is employed. A truncated ball which is of a slightly higher indexthan the crystal and which spacing is exactly set by its tolerances ofthickness allows the 57 degree internal half angle rays to come out at45 degrees (nominally) and be more easily collected and utilized.

FIG. 12 shows an end view of a luminescent rod 1250 excited by twoarrays of LEDs 1230 in which there is a column of forced air 1210 thatforced between the luminescent rod 1250 and the LED surface 1240 througha controlled airspace according to an embodiment of the invention. TheLED 1230 is bonded to a metal core circuit board 1220 which acts as aheat sink and a wire bond 1260 between the LED 1230 and the circuitboard 1220.

In an embodiment of the invention, the magnification can then be furtheroptically corrected to a perfect collimation, which can becolor-combined using standard dichroic edge combiners and recondensed toa spot. In an embodiment of the invention, the spot can be a liquidlight guide. In an alternative embodiment of the invention, the spot canbe a fiber bundle. In another embodiment of the invention, the spot canform the pupil of a Kohler illuminator.

In an embodiment of the invention, a desirable high efficiency andhighly effective illumination system for fluorescent microscopy can beformed by this color combined section in combination with the optics forKohler adaptation.

In an embodiment of the invention, the etendue of a single LED can beperfectly matched to the etendue of a liquid light guide. Assuming 1×1mm LED and 3 mm entrance guide, the numerical aperture (NA) can be inthe range from 0.2 up to about 0.6 which can be coupled to themicroscope by said Kohler adapter. In an alternative embodiment of theinvention, the image of the lightsource at the refocused spot can bescrambled or made homogeneous by means of a integrating or mixing rod ora mirror tunnel, which can be then be used within an Abbe illuminationsystem.

Many other applications exist for a portable, directly computercontrollable, easily spectrally tunable (by filter selection) lightsources of medium to very high brightnesses.

The distance between lenses in the Kohler setup is 95 mm and from LEoutput to Isuzu is 10 mm (1 mm shorter than the natural BFL).

Example 1

In an embodiment of the invention, a rod with 0.8 mm squarecross-section is coupled to a truncated ball lens and further magnifiedby a small plano-convex lens, finally collimated by a 38 mm focal length(FL) asphere. Allowing for two dichroic combining mirrors leaves an airspace of 68 mm. The energy can be refocused with another asphere, into a3 mm liquid light guide with an effective 0.3 NA.

FIG. 14 shows that at the refocus, a rectangular image of about 3.6 mmsquare is obtained; appropriate for alignment and optical tolerancebuildups.

FIG. 13 shows that launching rays within 55 degrees in the YAG, 40% canbe transferred into the LLG. In FIG. 15, a representative output from afour color light engine is provided. The specific colors (solid line)shown are UV 1510 (395 nm), 1520 Cyan (485 nm), 1530 Green (560 nm), and1540 Red (650 nm). Such a range of colors can be generated by acombination of diode lasers, LEDs and luminescent light pipes. The bandpositions and bandwidths for each color can be adjusted for a specificapplication. The output can consist of just color or a mix of colorsturned on in any order with any intensity for any length of time.

The output of the light engine can be used to excite any fluorescentlabel. The specific colors shown are particularly well suited to exciteDAPI, FITC, Cy3 and Cy5, respectively, because these colors overlap wellthe absorption bands of the labels. Other dyes can also be excited bythese colors. The light engine can be engineered to generate a differentmix of colors needed to excite labels with different absorption bands.

In standard fluorescence analysis, the emission from each label isfiltered by an emission filter before being recorded by a detector suchas a CCD camera. In FIG. 15, the profile for a four band emitter isshown (dotted line). The spectral output of the light engine isprecisely aligned with the emission filter so that the labels areexcited and fluorescence is detected with maximum signal to noise.

The output of the light engine can be engineered for a specific emissionband filter or collection of emission band filters to realize maximumsignal to noise. Maximum signal is achieved by maximizing thefluorescence signal level which is due the absorbance of the excitationlight and bandwidth of the emission filter. Minimum noise is realized byincorporating bandpass filters in the light engine (shown in FIG. 14).In this manner, the excitation light is typically reduced by 6 to 12orders of magnitude at the detector

FIG. 16 shows a representative output from a six color light engineaccording to an embodiment of the invention (FIG. 13). In FIG. 16, thespecific colors shown are 1610 UV (395 nm), 1620 Blue (445 nm), 1630Cyan (475 nm), 1640 Green (542 nm), 1650 Yellow (575 nm) and 1660 Red(650 nm). In various embodiments of the invention, a range of colors canbe generated by a combination of diode lasers, LEDs and luminescentlight pipes. In various embodiments of the invention, the band positionscan be adjusted for a specific application. In various embodiments ofthe invention, the bandwidths for each color can be adjusted for aspecific application. In various embodiments of the invention, theoutput can consist of just color or a mix of colors. In variousembodiments of the invention, the output can be turned on in any orderfor any length of time. In various embodiments of the invention, theoutput intensity can be varied for any length of time.

The far field (1 m distant) shows that an NA of about 0.31 can befilled.

The etendue of the rod is approximately 4.74 whereas the etendue of thetarget liquid light guide, restricting the NA output to 0.30 is a valuearound 1.9. A collection efficiency of 40% is the most which can beexpected. The rod is slightly oversized (86% is the maximum for circularcollection from a square).

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

1. An illumination system, comprising: a first light source, wherein thefirst light source is selected from one of a first Light Emitting Diode(LED) and a laser, wherein the first light source emits a first light ofa first color; and a luminescent rod light source, wherein theluminescent rod light source includes: a second LED light source,wherein the second LED light source emits a second light of a secondcolor; and a luminescent rod that is positioned to receive the secondlight, wherein the second light is absorbed by the luminescent rod whichthen emits a third light of a third color; an outlet aperture whereinthe third light exits at the outlet aperture; an optical element toincrease the light emitted at the outlet aperture; and associatedoptics, wherein the associated optics combine the light of the firstlight source and the light of the third light source on the same opticalaxis.
 2. The illumination system of claim 1, further comprising a fourthlight source, wherein when the fourth light source is selected from aLED and a laser, wherein the fourth light source emits a fourth light ofa fourth color, wherein the associated optics combines the light of thefirst light source, the light of the third light source and the light ofthe fourth light source on the same optical axis.
 3. The illuminationsystem of claim 1, further comprising one or more additional lightsource, wherein the additional light source is selected from a LED, alaser and a luminescent rod light source wherein the one or moreadditional light source emits one or more light of one or more color,wherein the associated optics combines the light of the first lightsource, the light of the third light source and the light of the one ormore additional light source on the same optical axis.
 4. Theillumination system of claim 1, further comprising an optical element tocouple the third light emitted from the luminescent rod at the outletaperture to a system that uses one or both the first light and thirdlight of the illumination system.
 5. The illumination system of claim 1,further comprising an optical element to couple the third light emittedfrom the luminescent rod into air within a 45 degree half-angle cone. 6.The illumination system of claim 1, wherein the luminescent rod has aproximal and a distal end, wherein the second LED light is adjacent theproximal end of the luminescent rod, wherein the third light is emittedin a forward direction and in a backward direction within theluminescent rod, further comprising an optical element positioned at theproximal end of the luminescent rod, wherein the first optical elementreflects the fluorescent light toward the distal end.
 7. Theillumination system of claim 1, wherein a plurality of LED light sourcesemit one or both the first light and the second light.
 8. Theillumination system of claim 1, wherein the second LED light passesthrough a plurality of luminescent rods arranged in series or inparallel.
 9. The illumination system of claim 1, wherein the thirdsecond selected color is between: an upper limit of 650 nm; and a lowerlimit of 450 nm.
 10. The illumination system of claim 1, wherein thesecond LED light passes through a plurality of luminescent rods.
 11. Amethod of generating light, comprising the steps of: applying a firstpotential to a first light source, wherein the first light source isselected from one of a first Light Emitting Diode (LED) and a laser,wherein the first light source emits a first light of a first color;applying a second potential to a second LED to generate second light ina second color; positioning a luminescent rod to receive the second LEDlight, wherein the second light is absorbed by the luminescent rod whichthen emits a third light of a third color, wherein the third light exitsat a outlet aperture; using an optical element to increase the lightemitted at the outlet aperture; and combining the first light and thethird light on the same optical axis.
 12. The method of claim 11,further comprising one or more light source, wherein the additionallight source is selected from a LED, a laser and a luminescent rod lightsource wherein the one or more additional light source emits one or morelight of one or more color, wherein the associated optics combines thelight of the first light source, the light of the third light source andthe light of the one or more additional light source on the same opticalaxis.
 13. The method of claim 11, wherein the luminescent rod has anoutlet aperture, further comprising an optical element to increase thelight emitted at the outlet aperture.
 14. The method of claim 11,wherein the luminescent rod has an outlet aperture, further comprisingan optical element to couple the third light emitted from theluminescent rod at the outlet aperture to a system that uses one or boththe first light and third light of the illumination system.
 15. Themethod of claim 11, further comprising an optical element to couple thethird light emitted from the luminescent rod into air within a 45 degreehalf-angle cone.
 16. The method of claim 11, wherein the luminescent rodhas a proximal and a distal end, wherein the second LED light isadjacent the proximal end of the luminescent rod, wherein the thirdlight is emitted in a forward direction and in a backward directionwithin the luminescent rod, further comprising an optical elementpositioned at the proximal end of the luminescent rod, wherein the firstoptical element reflects the fluorescent light toward the distal end.